Accumulator



June '26, 1945.

J. w. WHl T E ACGUMULATOH Original Filed' Sept INVENTOR. JOHN W. WHITEATTO NEY Reissued June 26, 1945 ACCUMULATOR John W. White, Van Nuys,Calif., assignor, by mesne assignments, to Bendix Aviation, Ltd., NorthHollywood, Calii'., a corporation of California Original No. 2,349,321,dated May 23, 1944, Serial No. 456,948, September 1, 1942. Applicationfor reissue February 16, 1945, Serial No. 578,142

2 Claims.

This invention relates to accumulators, particularly of the type used onthe hydraulic systems of airplanes.

An accumulator is a device for storing hydraulic fluid under pressure.This is done by providing a pressure vessel with a-yielding wall. Forthis purpose, a pressure vessel may be used having a yielding diaphragmagainst which the hydraulic fluid acts, with air or other gas undercompres sion acting'on the other side of the diaphragm. The diaphragmseparates air and liquid to prevent air from being dissolved in theliquid, which air might later cause trouble. Another type is an airbiased accumulator of the bladder type, in which a bladder fitted insidea pressure vessel is filled with air under compression against withhydraulic fluid acts. This type of accumulator is much lighter than thediaphragm type.

Athough this invention is fully applicable to a diaphragm typeaccumulator, or other type using compressed gas as a biasing means, itwill be described with relation to a bladder type accumulator.

One of the test requirements of all air biased accumulators used inaircraft is that the partition between air and hydraulic fluid must beable to withstand full hydraulic pressure when all the air is completelyexpelled from the unit. This test is to insure that the accumulator willnot be damaged by a faulty air valve. When all air is expelled thehydraulic pressure forces the bladder or diaphragm against the upperwalls of the accumulator, and against the air inlet hole.

Since bladders and diaphragms must be flexible, they are made of oilresisting synthetic rubber, such as Neoprene. This rubber is relativelytough, but not tough enough to prevent being extruded into the air inlethole under test conditions. The hydraulic test pressure used is about3,000 p. s. i. for 1,000 p. s. i. hydraulic systems. For hydraulicsystems of 3,000 p. s. i. this test pressure is 6,000 p. s. i. drilledholes are used for the air inlet, this pressure is sufficient to extrudethe rubber into the holes, cutting holes in the bladder or diaphragm,which completely unfits it for use.

Even if a group of fine part of shell I is a collar l2.

terial that will support. a bladder or diaphragm under pressure,

The drawing forming a part of this specification is an elevation ,view,in full section, of a bladder type accumulator embodying the invention.

- Referring to the drawing, a generally spherical shell III has fineholes22 drilled in the bottom thereof. A threaded fitting 24 is weldedtothe outside of the shell and the hydraulic system is connected to thisfitting. Welded to the upper The collar l2 has a threaded opening I4, aninternal annular shoulder I6 and an internal annular lip IS.

A bladder 26 of flexible material is fitted. in shell Ill. The bladder26 has a preformed shape as shown in solid lines, with the lower halfthinner than the upper half. The bladder has an internal bead 21, apatch 29 on the bottom, and has-an external lip 28 which hooks over'collar li ID. A plug 30 is fitted in collar H which fits snugly againstthe upper end of the bladder and rests upon shoulder I 6. 'An annularnut 32 is threaded within collar I2 to hold the plug 30 in place Acotter pin 34 passes through collar I2 and fits in a slot 36 in nut 32to lock the nut in place.

Plug 30 is centrally drilled at 40 to receive -a threaded air valve unit42. The hole 40 is enlarged at the bottom surface of plug 30 to receivean insert 44 of sintered powdered metal. The insert is composed ofbronze metal'sintered at I just below the eutectic temperature of thealloy.

It is therefore an object of this invention to provide an accumulatorhaving an air inlet which will not damage diaphragms and bladders whenfull hydraulic pressure is applied and the air expelled.

Another object is to provide an accumulator air inlet made ofsinteredpowdered metal.

Still another object is to cover an opening into the shell of anaccumulator with a porous ma- The pores in the metal are less thantwo-thousandths of an inch and probably average abouthalf of athousandth of an inch. These holes are so fine that they may beconsidered to be an impervious wall as regards a material having thetoughness of synthetic rubber at hydraulic test pressures. The air,however, has no difiicultyin passing through the sintered metal.

The hydraulic outlet 24 can also be provided with a'p'orous insert. Theresistanceto hydraulic fluid fiow is so much greater, however, than theresistance to air flow that it is not practical in all cases. I

In operation, air under pressure is applied at valve 42 and passesthrough porous insert 44 into the interior of bladder 26. The pressureis built up to about 600 p. s. i. The bladder 26 at this time is tightlypressed against the walls of shell HI, and the patch 29 of fabricmaterial on the bottom of bladder 26 covers hydraulic holes 22. Thepatch 29 is sufiicient to protect the bladder from extrusion throughdrilled holes inasmuch pressure systems.

Fitting 24 is then connected to a hydraulic system having a pump whichforces hydraulic fluid into the shell l0 against the air pressure. Asthe hydraulic flow increases, the lower part of bladder 28 will bepressed upwardly until the compression of the air builds up an airpressure which equals the hydraulic pressure. Thereafter the hydraulicfluid will be decreased or increased in amounts depending upon thedemands of the hydraulic system and the pump supply pressure. Fortesting, the air valve 42 is released, allowing all air to escape. Thehydraulic fluid causes the bladder to collapse. The lower half of thebladder being thinner than the upper half will collapse first,protruding upwardly into the upper half. When completely collapsed, thelower half will be inverted upon the upper half of the bladder as shownin dotted lines. The internal bead 21 on bladder 26 provides a radiusfor the bend so that the bladder material will not be too greatlystretched, an important point when the assembly is extremely cold andthe rubber is brittle. The

bladder also covers the bottom surface of plug ill and the insert 4|.

The insert 44 has such fine holes that as regards a material as tough asrubber, it presents an impervious or solid wall giving complete support.

' The invention therefore absolutely insures that the bladder 25 willnot be damaged.

. Having fully described the invention, it is not intended to limit itto the description or to the drawing or otherwise limit therinventionexcept by the terms of the following claims:

I claim:

l. Avbladder type accumulator comprising a shell having an air openingand a hydraulic opening, a flexible partition secured within said shellseparating said air opening from said hydraulic opening, and an insertof powdered metal placed in the inner end of said air opening havingaporosity that permits the passage of air, but of suflicient density topresent a surface that is impervious to the flow of partition material.to

protect said partition from damage when air is substantially lacking onone side of said partition and hydraulic pressure is applied on theother side of said partition.

' 2. accumulator comprising: a shell having two fluid openings, 9.flexible partition within said shell separating said openings, and aporous insert of powdered metal in one at-least of said openings, andhaving its inner surface substantially continuous with the inner surfaceof the adjacent portion of the shell, said insert having a porosity thatpermits the passage of fluid but being of sufilcient density to presenta surface that is impervious to said flexible partition to protect saidpartition from damage when fluid pressure is substantially lacking insaid one opening and high fluid pressure is applied through the otheropening to the other side. of said partition.

JOHN W.WHITE.

